tipc: remove interface state mirroring in bearer

struct 'tipc_bearer' is a generic representation of the underlying
media type, and exists in a one-to-one relationship to each interface
TIPC is using. The struct contains a 'blocked' flag that mirrors the
operational and execution state of the represented interface, and is
updated through notification calls from the latter. The users of
tipc_bearer are checking this flag before each attempt to send a
packet via the interface.

This state mirroring serves no purpose in the current code base. TIPC
links will not discover a media failure any faster through this
mechanism, and in reality the flag only adds overhead at packet
sending and reception.

Furthermore, the fact that the flag needs to be protected by a spinlock
aggregated into tipc_bearer has turned out to cause a serious and
completely unnecessary deadlock problem.

CPU0                                    CPU1
----                                    ----
Time 0: bearer_disable()                link_timeout()
Time 1:   spin_lock_bh(&b_ptr->lock)      tipc_link_push_queue()
Time 2:   tipc_link_delete()                tipc_bearer_blocked(b_ptr)
Time 3:     k_cancel_timer(&req->timer)       spin_lock_bh(&b_ptr->lock)
Time 4:       del_timer_sync(&req->timer)

I.e., del_timer_sync() on CPU0 never returns, because the timer handler
on CPU1 is waiting for the bearer lock.

We eliminate the 'blocked' flag from struct tipc_bearer, along with all
tests on this flag. This not only resolves the deadlock, but also
simplifies and speeds up the data path execution of TIPC. It also fits
well into our ongoing effort to make the locking policy simpler and
more manageable.

An effect of this change is that we can get rid of functions such as
tipc_bearer_blocked(), tipc_continue() and tipc_block_bearer().
We replace the latter with a new function, tipc_reset_bearer(), which
resets all links associated to the bearer immediately after an
interface goes down.

A user might notice one slight change in link behaviour after this
change. When an interface goes down, (e.g. through a NETDEV_DOWN
event) all attached links will be reset immediately, instead of
leaving it to each link to detect the failure through a timer-driven
mechanism. We consider this an improvement, and see no obvious risks
with the new behavior.

Signed-off-by: Erik Hugne <erik.hugne@ericsson.com>
Reviewed-by: Ying Xue <ying.xue@windriver.com>
Reviewed-by: Paul Gortmaker <Paul.Gortmaker@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 5 deletions

diff --git a/net/tipc/bearer.h b/net/tipc/bearer.h
index e5e04be..cc780bb 100644
--- a/net/tipc/bearer.h
+++ b/net/tipc/bearer.h
@@ -108,7 +108,6 @@ struct tipc_media {
  * struct tipc_bearer - TIPC bearer structure
  * @usr_handle: pointer to additional media-specific information about bearer
  * @mtu: max packet size bearer can support
- * @blocked: non-zero if bearer is blocked
  * @lock: spinlock for controlling access to bearer
  * @addr: media-specific address associated with bearer
  * @name: bearer name (format = media:interface)
@@ -130,7 +129,6 @@ struct tipc_media {
 struct tipc_bearer {
 	void *usr_handle;			/* initalized by media */
 	u32 mtu;				/* initalized by media */
-	int blocked;				/* initalized by media */
 	struct tipc_media_addr addr;		/* initalized by media */
 	char name[TIPC_MAX_BEARER_NAME];
 	spinlock_t lock;
@@ -163,8 +161,7 @@ int tipc_register_media(struct tipc_media *m_ptr);
 
 void tipc_recv_msg(struct sk_buff *buf, struct tipc_bearer *tb_ptr);
 
-int  tipc_block_bearer(struct tipc_bearer *b_ptr);
-void tipc_continue(struct tipc_bearer *tb_ptr);
+int  tipc_reset_bearer(struct tipc_bearer *b_ptr);
 
 int tipc_enable_bearer(const char *bearer_name, u32 disc_domain, u32 priority);
 int tipc_disable_bearer(const char *name);
@@ -194,7 +191,6 @@ void tipc_bearer_remove_dest(struct tipc_bearer *b_ptr, u32 dest);
 struct tipc_bearer *tipc_bearer_find(const char *name);
 struct tipc_bearer *tipc_bearer_find_interface(const char *if_name);
 struct tipc_media *tipc_media_find(const char *name);
-int tipc_bearer_blocked(struct tipc_bearer *b_ptr);
 void tipc_bearer_stop(void);
 
 /**